This invention relates generally to systems for inspecting printed circuit boards, and more particularly, to improved illumination and processing techniques for use in conjunction with systems of this general type.
As is well known to persons skilled in the art, a printed circuit board is used for mounting and electrically interconnecting electrical components in a predetermined manner. To the extent possible, such printed circuit boards are constructed mechanically, using automated assembly machines which operate to reduce the often prohibitive costs of manually assembling a printed circuit board. While reducing overall costs, such automated assembly techniques have been found to give rise to a certain limited degree of assembly defects such as mis-insertions of components, and their leads or pins, as well as defects in the soldering procedures which would then follow.
Originally, steps were taken to locate assembly errors of this general type through a visual inspection of each printed circuit board at a desired stage of the manufacturing process, by human operators using the naked eye, or possibly a stereo microscope or the like. However, since this procedure was found to be extremely tedious and inaccurate, as well as a relatively expensive process, steps were taken to develop automated systems for inspecting printed circuit boards, to replace such visual inspections.
Examples of devices of this general type are the Model 5511 and Model 5512 Printed Circuit Board Inspection Systems which are manufactured by Cimflex Teknowledge Corporation of Princeton, N.J. These inspection devices generally employ a series of cameras which are mounted within a fixture (an inspection head) adapted for controlled movement relative to a printed circuit board. The inspection head is either sequentially advanced to successive viewing fields (typically 1 inch by 1 inch) established along the surface of the printed circuit board then under inspection, or continuously advanced along the surface of the printed circuit board, to acquire images for microprocessor analysis. Any detected defects are in turn reported to the operator, for appropriate correction.
Further detail regarding the techniques which are used to perform these inspections are disclosed in U.S. patent application Ser. No. 07/159,774, entitled "Apparatus for Inspecting Printed Circuit Boards with Surface Mounted Components", the subject matter of which is incorporated by reference as if fully set forth herein. As disclosed, the accuracy of the inspection process can be enhanced by providing an inspection head which incorporates a series of four angled, orthogonally placed cameras, operated in conjunction with a selectively controllable light source. Through selective control the series of cameras, a variety of testing procedures are enabled including a verification of the placement of components (and their leads or pins), both before and after the soldering procedure, as well as a verification of the solder connections which are made.
Previously, this was accomplished by selectively activating one of eight lighting groups provided in a generally cylindrical fixture surrounding the series of cameras used to acquire images for inspection purposes. While adequate for its intended purpose, such illumination was found to be somewhat limiting in the patterns of light which could be developed. Essentially, this was limited to the availability of either a "high" lighting group or a "low" lighting group for each of the four cameras associated with the system's inspection head.
Thus, while such lighting was found to be effective in illuminating the printed circuit board to obtain the information needed to make a proper inspection of its condition, it nevertheless became desirable to develop a more versatile lighting system for use in performing such inspections.